The present invention relates to a clock recovery system for a TDMA (time division multiple access) satellite communication system. The present system is used at the receiving side of a satellite communication system.
In a TDMA system, a digital signal in bursts is transmitted periodically at a predetermined interval. At the receiving side, a clock signal for demodulating data must be recovered by using the information contained in the received burst itself.
Conventionally, that clock signal has been recovered in each related burst. That is to say, a clock signal for demodulating data of a burst is recovered by using said burst itself.
FIG. 1 shows a prior frame structure, in which the symbols (a), (b), (c) and (n) are bursts, and a.sub.1 through a.sub.5 shows the detail of each burst. The symbol a.sub.1 indicates guard time, a.sub.2 indicates carrier recovery symbols, a.sub.3 indicates clock recovery symbols usually has a pattern of alternating 1 and 0, a.sub.4 indicates UW (unique word), and a.sub.5 indicates data to be transmitted. The carrier recovery symbols a.sub.2 usually includes 40 symbols, and the clock recovery symbols a.sub.3 usually includes 80-150 symbols for establishing the synchronized clock signal with small phase error.
The disadvantage of a prior clock signal recovery system is that the clock signal a.sub.3 in a burst occupies a substantial time ratio in a burst. Since the necessary number of pulses of clock signal is fixed to 80-150 regardless of TDMA bit rate, that ratio is high in particular when the burst length is short, and the transmission speed is low, and the high ratio of clock recovery symbols in a burst decreases the transmission efficiency in a TDMA system.